WAEC Chemistry 2020 Paper

Concept:An anion is formed when an atom gains extra electrons, so its total electron count increases by the magnitude of the negative charge.Explanation:For a neutral phosphorus atom, the atomic number is $15$, so it contains $15$ electrons.The species given is $\mathrm{P}^{3-}$, which means it has gained $3$ extra electrons.Therefore, the total number of electrons is:$15 + 3 = 18$ electrons.Answer:D. $18$